Hi Olivia! Here is a list of my faves:
I wear a size small in most brands (if that's helpful for you)
Outdoor Voices: Tech Sweat
Nike: The new "Luxe" leggings are awesome
Lululemon: Align II and Wunder Under
Tip: I buy most of my clothes off Poshmark! Just search (for example) "Outdoor Voices + Tech Sweat" and you can usually find clothing that is gently worn, if not new. Hope that helps!